Magnetic field induced emergent inhomogeneity in a superconducting film with weak and homogeneous disorder

TL;DR

This paper demonstrates that in weakly disordered superconducting films, an applied magnetic field induces a granular state with vortex-separated islands, leading to a pseudogap phase before complete superconductivity destruction.

Contribution

It reveals a novel field-induced inhomogeneity and pseudogap phase in weakly disordered superconductors, differing from the traditional vortex overlap mechanism.

Findings

Superconducting state becomes granular under magnetic field.

Vortex lines separate superconducting islands.

A pseudogap phase emerges with destroyed global coherence.

Abstract

When a magnetic field is applied, the mixed state of a conventional Type II superconductor gets destroyed at the upper critical field Hc2, where the normal vortex cores overlap with each other. Here, we show that in the presence weak and homogeneous disorder the destruction of superconductivity with field follows a different route. Starting with a weakly disordered NbN thin film ( Tc ~ 9K ), we show that under the application of magnetic field the superconducting state becomes increasingly granular, where lines of vortices separate the superconducting islands. Consequently, phase fluctuations between these islands give rise to a field induced pseudogap phase, which has a gap in the electronic density of states but where the global zero resistance state is destroyed.